Trammel bar compass



Jan. 20, 1959 J. M. BERGE TRAMMEL BAR COMPASS Filed Spt. 17, 1956 AAAA-IN VEN TOR. J0551 1! l7. Bazae United States Patent TRAMMEL BAR COMPASSJoseph M. Berge, San Clemente, Calif. Application September 17, 1956,Serial No. 610,311

1 Claim. (Cl. 33-27) This invention relates to drafting instruments andin particular to compasses of the trammel bar type, wherein center pointand lead holders respectively are attached to respective ends of atrammel bar in a manner to be adjustable longitudinally thereof forsetting the radius of a circle to be scribed.

The invention has as its primary object to provide improvements in thistype of compass. In particular, the invention contemplates an improvedslider and chuck unit embodying parts having improved grippingqualities. More particularly, the invention contemplates a sliderembodying a collet, fabricated from a soft plastic material such as anylon resin, providing improved gripping attachment to the trammel barwhen the collet is tightened, and also embodying improved wearingqualities to avoid the development of looseness over an extended periodof use.

Another object is to provide a chuck for a center point or lead,embodying an improved collet of a plastic material such as thatindicated above, having improved gripping qualities in securing a centerpoint or lead in such collet.

A further object is to provide an improved arrangement of spring loadedslider with vernier adjustment for fine adjustment of the spacingbetween center point and lead.

Another object is to provide an improved slider and collet unitembodying storage space for extra lead and center points.

Other objects will become apparent in the ensuing specifications andappended drawings in which:

Fig. l is a side view, partially broken away and in section, showing oneend of a compass embodying my invention;

Fig. 2 is a view of the same side of the compass, partially broken awayand in section, showing the other end of the compass;

Fig. 3- is a front sectional view of the slider collet, taken on theline 33 of Fig. 1;

Fig. 4 is an end view of the same, partially in section, taken on theline 44 of Fig. 1;

Fig. 5 is an enlarged detail exploded view of the slider collet, withparts broken away and shown in section;

Fig. 6 is an enlarged detail view, partially in section, of the slidercollet and an associated section of the trammel bar;

Fig. 7 is an enlarged fragmentary detail side view of the spring loadingportions of the vernier-adjusted slider unit;

Fig. 8 is a cross-sectional view of the same;

Fig. 9 is a detail enlarged sectional view of the vernier portionthereof;

Fig. 10 is an exploded side view partially in section, of one of thepoint holding collets;

Fig. 11 is a detail axial sectional view of the assembled point holdingcollet; and

Fig. 12 is a cross sectional view thereof taken on the line 12-12 ofFig. 11.

Referring now to the drawing in detail, I have shown, as an example ofone form in which the invention may be embodied, a trammel bar type ofcompass embodying, in general, a trammel bar 12, a manually adjustableslider and collet unit 13 on one end of bar 12, and a vernier adjustmentslider unit 14 on the other end of the bar 12. Unit 13 is adapted to beloosened, slid bodily to any selected position along the length of bar12 short of the unit 14, and locked to the bar in the selected position.Fine adjustment of the spacing between the two units is then obtained byadjusting the vernier unit 14.

Each of the end units 13 and 14 includes identical sub units as follows:a sliderblock 16 is slidably mounted on the tramrnel bar 12 and isprovided with a collet unit 17 for locking it to the bar 12. Similarslider block and collet parts are indicated at 16 and 17' in the unit14. A point holding chuck unit 18' is attached to slider block 16.

Slider blocks 16, 16 are fabricated of a very tough, durable, longwearing plastic material of the group including the nylon (polyamide)and Teflon (tetrafluoroethylene) resins and since the nylon resin is theless expensive of the two, it is preferred. Such a resin providessmooth, slick surfaces within the passage 19, of

cross section corresponding to that of trammel bar 12,'

which extends lengthwise through the central body 20 of slider block 15,16 through a collet neck 21 which is formed integrally with one end ofbody Ed, and through collet jaws 22 which are formed integrally with theend or neck 21 and project therebeyond in coaxial relation thereto. laws22 are circumferentially separated by slots 23 so that the jaws can bedeflected inwardly into gripping engagement with the faces of bar 12 bythe wedging action of a conventional collet nut 24- which is threadedonto an external thread 25 on neck 21. To this end, the nut 2% has theconventional frusto-conical throat 26 for engagement with jaws 22.

Tramrnel bar 12 is of non-circular cross section, and is preferablysquare although it may be hexagonal or other prismatic cross section.The passage 19 is of corresponding cross section and fitted fairlyclosely to the bar 12. When jaws 22 are tightened against the bar 12,all such looseness is completely eliminated by the engagement of theflat inner faces of jaws 22 with the correspondingly llat faces of thebar 12.

When the collet nut 24 is loosened, the smooth internal surfaces of thesliders 16, is allow them to be freely slide along the bar 12 to newpositions.

Referring now to the point chucking units 18 and 18, each of these unitsincludes a coupler nut 27 which is threaded onto a threaded coupler neck28 formed as an integral portion of the slider body 211 and projectingat right angles to the neck 21. Coupler nut 27 includes an internallythreaded skirt portion 29 which received the neck 23, a reduced tipportion 33 which has a cylindrical bore 31 therein, and a frusto-conicalthroat 32 extending between the bore 31 and the internally threaded boreof skirt portion 2%. Received in neck 27 is a chuck sleeve 33 includinga cylindrical intermediate body portion, an enlarged head 34 received inthroat 32 and having a frusto-conical shoulder fitted thereto, and atapered collet tip 35 at its opposite end, projecting beyond the end ofnut 319 and having a reduced bore 36 to receive a lead point 37 (unit1'3) or a center point 38 (unit 14). A look nut 39 is threaded ontocollet tip 35 and engages with collet jaws at the end thereof to tightenthe same against the point 37 or 38 in accordance with conventionalsub-structure in drawing instruments.

Tubular body 33 has an enlarged bore 40 which registers with a bore 41of the same diameter in neck 28. The bores 40 and 41 cooperativelydefine a storage chamber for extra lead points and center points in therespective chuck units 18, 18.

The chuck sleeve 33 is of a nylon or Teflon material adapted to provideimproved gripping of the lead point 37 and center point 33. Head 54- hasa fiat end which abuts a squared end on neck 23 and is tightenedthereagainst when nut 27 is drawn tight on neck 28. Additional lockingefiect is attained by the frictional engagement of throat 32 against theconforming shoulder on head 34, plus the engagement between collar andneck 28. The locking of sleeve 33 to body is necessary before collet nut39 can be rotated upon sleeve 33. Improved gripping of the chuck body 33to the neck 28 is provided by engagement of the two like plasticsurfaces under pressure. Nuts 27 and 24 are of metal for facilitatingthe rotation of the threaded parts relative to one another. Nut 39 onthe other hand is of the plastic material, and is inexpensively producedby a molding operation.

Referring now to the Vernier unit 14, this unit is interposed between avernier nut 42 which is threaded onto a threaded end portion 43 of bar12, and a coil spring 44 which abuts against a washer 45 in the form ofa snap ring (Fig. 8) inserted into a slot 46 extending around the bar12. Spring 44 is engaged under compression between washer 45 and the nut24 of collet unit 17'.

It will now be apparent that by rotating nut 42 on threaded shank 43 inan advancing direction, the slider unit 16' will be advanced toward theunit 13, compressing spring 44, and upon rotating nut 42 in a retractingdirection, spring 44 will move the unit 14 back toward the threaded end43 of the bar 12.

4 I claim: In a scribing compass of the trammel bar type: a trammel bar;and a pair of point carrying units attached torespective ends of saidbar; at least one of said point carrying units including a slider bodyof polyamide material siidably mounted on said bar and having externallythreaded collet jaws for clamping it to the bar in any selected positionof adjustment thereon, and a metallic collet nut threaded onto said jawsfor constricting the nto said clamping engagement; and a point holdinchuck unit attached to said slider body, said chuck unit including acoupler neck integral with said slider body and projecting at rightangles to the axis of said collet iaws, a metallic coupler nut threadedonto said coupler neck; a chuck body of polyamide material received insaid coupler nut and having an inner end in the form of a head inabutting relation to the end of said coupler neck and adapted to belocked thereto by tightening said coupler nut, and a point holding chuckon the outer end of said chuck unit.

References Cited in the file of this patent UNITED STATES PATENTS522,053 Gates June 26, 1894 534,152 Henkel Feb. 12, 1895 695,661Theibault Mar. 18, 1902 1,236,069 Duryea Aug. 7, 1917 2,046,508 FriessJuly 7, 1936 2,246,086 Austin June 17, 1941 2,419,752 Zumbuhl Apr. 29,1947 2,755,110 Jacobs July 17, 1956

